For this purpose, a scale embodiment configured as a measuring element, e.g. a measuring tape is applied to the circumference, typically the outer circumference of the measuring ring, typically in that the measuring tape is separately produced and subsequently fixated on the circumference of a support ring or a support wheel. It is also feasible to configure the scale embodiment directly on the support ring.
In this context, it is clear that a “ring” can also be a shaft or similar with a massive cross-section in case no inner diameter is required. Furthermore, subsequently, only a measuring tape is discussed without limiting the invention with respect to the measuring element which can also be a cable or similar.
The scale embodiments following one after another in circumferential direction can be configured through different physical principles, e.g. magnetically, optically or mechanically, and are scanned by a reading head through a suitable physical principle, wherein the reading head is arranged stationary at a location of the circumference and arranged at a distance from the measuring tape, thus touch-free when the circumference and thus the scale embodiment move past the reading head during a relative rotation of the measuring ring.
Thus, a preferred embodiment is the magnetic configuration of the scale embodiments.
Measuring wheels with predetermined nominal diameters are commercially available in which the scale embodiments, typically configured as a measuring tape are provided on the entire circumference of the measuring ring, preferably without gaps in order to be able to provide a scanning through the reading head over the entire circumference of the measuring ring.
In particular for magnetic scale embodiments, in particular for a measuring tape applied to the measuring ring, the measuring tape typically is a plastic-based material which is elastic with respect to mechanical loading in its longitudinal extension which has to be considered in particular during production. The measuring tape is also subject to length changes during temperature changes, which has to be considered in particular during operations of the measuring tape since the temperature expansion of the measuring tape is typically different from the temperature expansion of the material from which the support ring of the measuring ring is made and which is typically metal.
This difference in longitudinal extension has little effect for small diameters of the measuring ring so that also for small measuring wheels, a measuring tape of this type can be fixated over the entire circumference at the support ring, e.g. glued or vulcanized. The different length expansion, however, becomes a problem for measuring wheels and their support rings with large diameter, e.g. in the range of one meter and more, and in particular when the support ring is not a circumferentially closed ring, but has one or plural gaps in circumferential direction, e.g. because it has to be assembled from particular segments.
In this case, the measuring tape cannot be permanently connected over the entire circumference with the support ring and can in particular not be applied to the support ring without gaps, in particular not on both sides of a gap in the support ring which can also change its size through temperature- and operational influences.